By Alfred F. Wong, P.Eng., F.CSCE
CISC provides this column as a part of its commitment to the education of those interested in the use of steel in construction. Neither CISC nor the author assumes responsibility for errors or oversights resulting from the use of the information contained herein. Suggested solutions may not necessarily apply to a particular structure or application, and are not intended to replace the expertise of a professional engineer, architect or other licensed professional.
Question 1: Must the ends of compression members at a bolted splice be finished to bear?
Answer: While gravity column segments are usually finished to bear at splices, compression members generally need not be finished to bear provided the bolted splice is proportioned to resist the factored forces and effects without end bearing contribution. An example is shown in the Figure.
Question 2: : Are the factored resistances of Welded Unstiffened Angle Seats provided in Table 3-43 of the CISC Handbook applicable to beams with and without bearing stiffeners? How is the beam flange thickness, tb , determined?
Answer: The Table was developed for beams without bearing stiffeners. The beam flange thickness, tb , is approximated using the expression tb = 1.6w – 3, which has been derived from regression analysis and gives a very good estimate for rolled wide-flange beam sections. This eliminates the need to look up the value tb.
Question 3: Are UL listed fire-rated steel-framed floor designs as well as cUL listings, applicable in Canada? What is the difference?
Answer: The National Building Code of Canada, in Division B “Acceptable Solutions”, requires that fire-resistance ratings be determined in accordance with CAN/ULC Standard S101, “Fire Endurance Tests of Building Construction and Materials”. According to UL LLC, cUL listed designs comply with CAN/ULC S101 whereas UL listings were not tested to S101.
Question 4: Should I always specify the spray-applied fire-rated floor assembly design on design documents? May I simply specify the code required fire separation rating to permit multiple bids?
Answer: The regulatory authorities typically ask that the fire-rated listing(s) be specified on the design documents. Moreover, the listed design selection process serves to ensure that the prescriptive design rating is achievable. For example: do the open-web steel joists meet the minimum mass required for the common listings; is the slab thickness and concrete density combination compatible with common listed designs if an unsprayed deck design is desired?
In order to allow multiple bids and competitions among multiple fire-resistive material producers, one may specify several suitable listed design options. Alternatively, specify one design but allow equivalent listed designs in compliance with CAN/ULC S101. Part 1 of CISC Steel Design Series “ULC and cUL Sprayed-Applied Fire Rated Designs” includes a summary of popular rated designs for applications in Canada. https://cisc-icca.ca/cisc-steel-design-series/